m 
■ 



No. 9205 



■ 



I 
■ 

■ 






■ 

■ 











J 



H 







■ ■ 



Ml 



■ ■ 



■Wftwfl 



hh 






. »• ,G V *c» *?XT^ A <-. 



.0 



• . » • ,G r "o, **V.T* ' A 






•• "*b 






5 v> 

.A* .•^♦. 





V * ' * ° 



; %? 























oK 



°^ 






'oV 5 





i0* .ti^% "*> * V 



4. o 













^7 ^* » # K 



/ ♦♦*% 






^ oV^a'- *^v* -*w$^\ *+ Mt & 




*bV 



^•o^ 







.0^, *^Si^^* 4 ^^ " 



^v 












:t* a 




W 




^ c*^ 













g^.^:, \ /Vi^/V .g^.j^.% .^^^c/V g ^. 





^ 










V •«• 




". ^o V^ 







^0^ ° 




v oV* 














^^ 
















r*° <?% . : 



v» 






^ v ^ 
-v v 



► V 








fe: %S M^°.\/ Sim: \S :m&: V/ ViSte- < 



A^ .!•'«„ "<£. 











• * * * ▼ -s. . \ *£* 







V 3 ^^ T ^ ^ 
4? % °y$Ws J* ^. 




r ^o x 






vv 





7« A 





-: 



••* ^ % -.jSk-' ♦* ** vWx /\ -far.- ♦♦*% 'if§f. ; #*% -.»»: *♦**+ 

y^Wty *.. v$IBv* \' -: ?P> ""X;^/ °v : S^> i0 "\ • 





A 6 -V *'TVT-- A 

0^ . • » • - *K~ A> 























.v^ 



.^^. 









V -O^ 



r°^ oil:* "*b aV 









v-s* 



'.'■- 



V 









8 A^ » 



«*v 



^^ :^l;^ 1 "^ -mem- ** »^ii^^ ^.^ 






^ 4o ^ 






^^ 



'^o A 



k 'T°: . * .<\ 



v, 




BUREAU OF MINES 
INFORMATION CIRCULAR/1988 




Emission Products From Combustion 
of Conveyor Belts 

By Margaret R. Egan 



UNITED STATES DEPARTMENT OF THE INTERIOR 




A£^&&"' $*^i / t^ 



Information Circular 9205 



Emission Products From Combustion 
of Conveyor Belts 

By Margaret R. Egan 



UNITED STATES DEPARTMENT OF THE INTERIOR 
Donald Paul Hodel, Secretary 

BUREAU OF MINES 
T S Ary, Director 



^2 



*fi 



<\ 



Z° 



^ 



Library of Congress Cataloging in Publication Data: 



Egan, Margaret R. 

Emission products from combustion of conveyor belts. 

(Bureau of Mines information circular; 9205) 

Bibliography: p. 11 

Supt. of Docs, no.: I 28.27:9205. 

1. Conveyor belts— Fire - testing. 2. Combustion gases— Analysis. 3. Smoke- 
Analysis. I. Title. II. Series: Information circular (United States. Bureau of 
Mines); 9205. 



TN295.U4 [TH9446.5.B44] 622 s [622'.8] 



88-600216 



CONTENTS 

Page 

Abstract 1 

Introduction 2 

Experimental equipment 2 

Intermediate-scale fire tunnel 2 

Data logging 2 

Instrumentation 2 

Thermocouples 2 

Flow probes and pressure transducers 2 

Gas monitors 2 

Smoke monitors 4 

Weight-loss monitor 4 

Typical test procedure 4 

Calculations 4 

Product generation rates 5 

Combustion yields 5 

Heat-release rates 5 

Production constants 5 

Smoke particle diameters 6 

Conveyor belt combustion results and discussion 6 

Gas concentrations and heat production 7 

Smoke characteristics 8 

Combustion yields 9 

Production constants 9 

Smoldering stage data 9 

Comparison of materials tested 10 

Considerations 11 

References 11 

Appendix-Symbols used in this report 12 

ILLUSTRATIONS 

1. Schematic of intermediate-scale tunnel 3 

2. Results of typical ignitable conveyor belt combustion experiment 7 

3. Extent of the combustion and charring for R5 8 

TABLES 

1. Heat release equation variables for conveyor belts 5 

2. Conveyor belts analyzed 6 

3. Gas concentrations, generation rates, and heat-release rates for conveyor belts 7 

4. Smoke characteristics for conveyor belts 8 

5. Mean particle sizes and smoke obscuration for conveyor belts 9 

6. Combustion yields for ignitable conveyor belts 9 

7. Steady-state production constants for conveyor belts 9 

8. Smoldering data for conveyor belts 10 

9. Ignition source and ventilation rates 10 

10. Gas, heat, and smoke concentrations 11 

11. Normalized gas and smoke concentrations 11 

12. Particle size and smoke obscuration 11 

13. Production constants 11 





UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 


cfm 




cubic foot per minute 


kW 


kilowatt 


cm 




centimeter 


m 


meter 


g 




gram 


m 3 /s 


cubic meter per second 


g/cm 3 




gram per cubic centimeter 


mg/m 3 


milligram per cubic meter 


g/g 




gram per gram 


min 


minute 


g/W 




gram per kilojoule 


/im 


micrometer 


g/(m 3 « 


ppm) 


gram per cubic meter times 
part per million 


p/cm 3 


particle per cubic 
centimeter 


g/s 




gram per second 


P/g 


particle per gram 


kg 




kilogram 


p/kJ 


particle per kilojoule 


W/g 




kilojoule per gram 


ppm 


part per million 



EMISSION PRODUCTS FROM COMBUSTION OF CONVEYOR BELTS 



By Margaret R. Egan 1 



ABSTRACT 



A series of experiments were undertaken by the Bureau of Mines to determine the emission products 
of several types of conveyor belting and other combustible materials found in mines. These experiments 
were conducted under intermediate-scale, simulated mine conditions to determine smoke characteristics 
and gas concentrations. From these determinations, heat-release rates, particle sizes, obscuration rates, 
combustion yields, and production constants were calculated. 

Three types of belts were investigated: chloroprene, also known as neoprene (NP); polyvinyl chloride 
(PVC); and styrene-butadiene rubber (SBR). The belts were designated as ignitable or self-extinguishing 
depending on the length of the burning time and the subsequent combustion products. Under these 
experimental conditions, the SBR belts were the easiest to ignite. The PVC and NP belts tended to self- 
extinguish within a few minutes after ignition, but were still capable of maintaining a brief flaming 
period. 

These conveyor belt combustion results are compared with previous analyses of wood, transformer 
fluid, and coal fires. Together they form a data base by which findings from future experiments with 
other mine combustibles can be compared. 



1 Chemist, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 



INTRODUCTION 



The Bureau of Mines conducts research to improve 
health and safety conditions in mines. Fires are 
particularly dangerous in underground mines because of 
the added threat of smoke and toxic gases being carried 
throughout the mine by its ventilation system. Therefore, 
the Bureau has analyzed the combustion emissions of 
materials found in mines. 

The objectives of this study were to measure the gas 
production and smoke characteristics of burning conveyor 
belts, and to compare these results with those of other 
combustible materials previously studied. Once the gas 



concentrations and smoke characteristics of combustible 
materials are determined, more efficient detection, 
suppression, and rescue equipment can be designed. 

This report supplements previous Bureau studies (1-3) 2 
of other combustible materials burned in a test apparatus 
designed to simulate a mine environment. This study 
focused on conveyor belting because of the significant 
quantities used and their possible location on the air-intake 
side of the ventilating system. Determining the fire 
resistance of conveyor belts was presented in a previous 
Bureau report (4), and was not part of this study. 



EXPERIMENTAL EQUIPMENT 



INTERMEDIATE-SCALE FIRE TUNNEL 

The conveyor belt fires were conducted in the Bureau's 
intermediate-scale fire tunnel. This tunnel has been 
shown (5) to successfully predict full-scale fire conditions. 
A schematic of the tunnel with its data-acquisition system 
is shown in figure 1. 

The tunnel is 0.8 m wide by 0.8 m high by 10 m long 
and is divided into several sections. The first horizontal 
section is cone-shaped and 1.5 m long. It is hinged and 
can be lifted to allow entrance into the tunnel for the 
placement of the belting. It begins with a cylindrical duct 
that is 0.25 m long by 0.3 m in diameter and gradually 
enlarges until it matches the tunnel dimensions. Next is 
the fire zone where the gas burner and the conveyor belt 



platform are located. The fire zone and the remaining 
horizontal section are lined with firebrick and contain the 
thermocouples, flow probes, and sampling ports. The 
diffusing grid begins the vertical section of the tunnel, 
which contains an adjustable orifice plate. The final 
section is horizontal and ends at an exterior exhaust fan. 

DATA LOGGING 

The tunnel was equipped with a 48-channel data 
collection system. A program was designed to scan, 
record, and calculate the data from all channels including 
a number of cross-channel calculations. These calculations 
and the raw voltage readings are stored, displayed, and 
updated every minute throughout the experiment. 



INSTRUMENTATION 



All instruments were periodically cleaned and calibrated 
according to manufacturers' instructions for the quantity of 
smoke and the amount of use each had received. 

THERMOCOUPLES 

Thermocouple arrays were located 1.57, 2.36, 3.15, 4.72, 
6.30, and 7.87 m from the gas burner. Additional 
thermocouples were located within the air-intake cone and 
near the exhaust fan. A total of 28 thermocouples were 
used to measure the temperature distributions resulting 
from the fires. Their locations are also shown in figure 1. 

FLOW PROBES AND PRESSURE TRANSDUCERS 

A bidirectional flow probe (6) in conjunction with a 
pressure transducer was used to determine velocity. The 
airflow was produced by the exhaust fan and was detected 
by the flow probe and converted to a linear electrical 
signal by the pressure transducer. This signal was then 
scanned, stored, and converted to cubic meter per second 
by the data collection system. The locations of all of the 



flow probes are shown in figure 1. The flow probe 
centered in the air-intake cylinder was used to obtain the 
velocity measurements. 

The stated error of the flow probe is ±7%. The 
pressure transducer introduces another possible error of 
±5.3%. Assuming the errors to be independently 
distributed, the compound error was estimated to be 
±8.8%. Averaging over 10 data points improves the 
precision by the square root of 10, resulting in a total 
estimated error of ±2.8%. 

Before each experiment, velocity readings were also 
made with a vane-type anemometer to insure that the air- 
intake velocity was approximately the same for all tests. 

GAS MONITORS 

The CO analyzer used measures accurately within 1% 
of full range or ±5 ppm. The C0 2 analyzer measures 
accurately within 1% of full range or ±250 ppm. These 

2 Italic numbers in parentheses refer to items in the list of references 
preceding the appendix at the end of this report. 



10m 



/0.61m -diam duct 



12 m 



f 



1.22m 

^ ^ /Conveyor /-0.8 m - square duct 
Fire zone — , /belt sample / 
Air . - ^ \A . .. ' . r 




Burner>^ Loadce|| 



0.305m- diam 
entrance duct 
hinged and movable^ 



SxIK 



^ 



Air 



/ exhaust 
-Manually Ventilation 
adjustable 
orifice plate 



Diffusing grid 



fan 
2-speed ) 



TEOM 



CNM 



CO meter 



CO2 meter 



Pressure transducers 



48- 
channel 
data- 
acqui- 
sition 
system 



3\ 
- detector 



f...28— f 
thermocouples 



-Load cell 

-Digital input 

for CNM 

range 



DECNET- 



PDP 
11/44 



Control 
terminal 



Printer 











VAX 
11/780 




CALCOMP 
plotter 








. 






VAX 

terminal 





Pressure transducer (flow probe) 
Differential pressure transducer 
3\ detector 
Thermocouples 
Sampling ports 



KEY 

CALCOMP California computer products 

CNM Condensation nuclei monitor 

DECNET Digital equipment networking 

PDP Programmed data processor 

TEOM Tapered-element oscillating microbalance 



VAX 



Virtual address extension 



Figure 1 —Schematic of intermediate-scale tunnel (top) and data-acquisition system (bottom). 



analyzers were calibrated at the beginning of each 
experiment. In addition, the concentrations of the span 
gases were independently analyzed at the beginning of 
each series of experiments. 

SMOKE MONITORS 

The particle number concentration (N ) was obtained 
with a condensation nuclei monitor (CNM), manufactured 
by Environment One Corp. 3 of Schenectady, NY. This 
monitor uses a cloud chamber to measure the 
concentration of submicrometer airborne particles (p). 
The particulate cloud attenuates a light beam which ulti- 
mately produces a measurable electrical signal. The 
accuracy is stated as ±20% of a point above 30% of scale 
within the linear range from 3,000 to 300,000 p/cm 3 . 
Therefore, in these experiments, the calculated error could 
have been as great as ± 18,000 p/cm 3 . 

To reduce the particulate count to within the range of 
the CNM, a 10% dilution of the smoke was necessary. 
Two flow meters, with a stated accuracy of ±2%, were 
used. One meter was used to measure the flow of the 
sample, and the other to measure filtered room air. 
Compounding these errors makes the CNM the least 
accurate of all the instruments at ±21%. The particle 
mass concentration (M ) was obtained by a 
tapered-element oscillating microbalance (TEOM) 
developed by Rupprecht & Patashnick Co., Inc. (7) of 
Voorheesville, NY. It measures the mass directly by 
depositing the particles on a filter attached to an oscillating 
tapered element. The oscillating frequency of the tapered 



element decreases as the deposited mass increases. The 
apparatus is capable of measuring the particulate concen- 
tration with a better than 5% accuracy at the level used. 
According to the manufacturer, the filter collects at least 
50% of all particles with a volume mean diameter of 
0.05 fim, with increasing collection efficiency as the 
diameter increases. Actual data obtained by the Bureau 
using particles of volume mean diameter equal to 0.048 /im 
indicated a collection efficiency closer to 90%. 

Since the diameter of average mass was calculated from 
the mass and number concentrations, its accuracy was 
dependent upon the precision of the TEOM and CNM. 
Considering the error band of the mass and number 
concentrations from the conveyor belt experiments, the 
diameter of average mass could vary by 10%. 

A three-wavelength-light transmission technique (8) 
developed by the Bureau was also used to measure particle 
size and smoke obscuration. White light was transmitted 
through a smoke cloud to the detector. The beam was 
split into three parts, and each passed through an 
interference filter centered at wavelengths of either 0.45, 
0.63, or 1.00 /im. Each photodiode output was amplified 
and the voltage was recorded. 

WEIGHT-LOSS MONITOR 

The weight-loss data were obtained by a strain-gauge 
conditioner in conjunction with a load cell that has a range 
up to 22.68 kg. Their combined accuracy is stated as 
0.05% of full scale or ± 11.3 g. 



TYPICAL TEST PROCEDURE 



The conveyor belt was located 43 cm from the ceiling 
of the tunnel. A 23- by 46-cm section was attached to a 
support that was six-legged and approximately 15 cm high. 
The support sat on a platform attached to a shaft 
extending through a hole in the tunnel floor. The shaft 
rested on a load cell so that continuous weight loss could 
be recorded. 

Prior to each experiment, background readings were 
obtained after the conveyor belting was positioned and the 
exhaust fan was started. All instruments were continuously 
scanned and recorded throughout the experiment. 



The belts were heated with a natural gas burner located 
immediately upstream of the belt. The burner flow rate 
was maintained at 7 cfm until the belt was ignited. The 
flame was perpendicular to the front end of the belt and 
was pulled over its surface by the ventilation. Once 
ignition occurred, the burner was turned off. The flames 
either spread along the top surface of the belt or 
extinguished within a few minutes. 



CALCULATIONS 



It is necessary to measure certain parameters in order 
to compare the active-burning combustion products and 
ultimately the hazards of various fuels. Among these 
measurements are gas concentrations, smoke particle mass 

3 Reference to specific products does not imply endorsement by the 
Bureau of Mines. 



and number concentrations, ventilation rate, and mass-loss 
rate. Other combustion properties can be calculated once 
these values are known. 



PRODUCT GENERATION RATES 



where Q A = actual heat release, kW, 



In a ventilated system, the generation rates (Gx) of C0 2 
and CO are related to the bulk average concentration 
increases above ambient air, ACO z and ACO respectively, 
by the expressions 



(1) 
(2) 



G C o 2 = Mc^xV^xACOj 
and G co = M co x V A x ACO, 

where M co = 1.97 x 10" 3 g/(m 3 »ppm), 

M co = 1.25 x 10" 3 g/(m 3 «ppm), 
and V A = incoming airflow, m /s. 

COMBUSTION YIELDS 



Once the generation rates are known and the mass-loss 
rate of the fuel (M() is calculated using the load-cell 
assembly, the yield of the combustion product ( YJ can be 
calculated by the expression 



Y x = G x /M f . 



(3) 



The yields for M and N are calculated in a similar 
manner by the expression 



Y x = AX (C X )(V A )/M f , 



(4) 



where 



and 



C x = appropriate units conversion factor: 
1.00 x 10 when M Q is in milligram 
per cubic meter or 
1.00 x 10 when N Q is in particle per 
cubic centimeter; 

AX = smoke concentration increase above 
ambient (when M Q is measured in 
milligram per cubic meter and N Q 
is measured in particle per cubic 
centimeter. 

HEAT-RELEASE RATES 



It has been shown (9) that the actual heat-release rate 
realized during a fire can be calculated from the 
expression 



Qa = 



l*coJ 



G co 2 + 



H c " H co (Kco) 



Kco 



G co . (5) 



H c = net heat of complete combustion of the 
conveyor belting, kJ/g, 

H co = heat of combustion of CO (10.1 kJ/g), 

I^o = theoretical yield of C0 2 , g/g, 

and I^Q = theoretical yield of CO, g/g. 

The H c and K^ values vary with the composition of the 
belt. The values, listed in table 1, were derived from the 
ultimate chemical analyses and the caloric values 
determined by an independent testing laboratory. The 
actual heat-release rates could be calculated by substituting 
the experimental values for V^, ACOj, and ACO and 
those from table 1 in equations 1, 2, and 5. The actual 
heat of combustion (H^ is lower than the net heat of 
combustion (H c ) since a typical fire rarely attains a state 
of complete combustion. 
H A can be calculated from the expression 



By measuring both Q A and M f , 



H A = Q A /M f . 



(6) 



This was only possible for the more easily ignited belts 
because the mass loss for the other belts was too small to 
be accurately determined. 

PRODUCTION CONSTANTS 

In an actual mine fire, it is difficult, if not impossible, to 
calculate the actual heat of combustion. Moreover, since 
determining the yield of a combustion product depends 
upon this information, significant errors can result in 
predicting the resultant concentration increases. For fires, 

TABLE 1. - Heat release equation variables for 
conveyor belts 



Sample 



H c , kJ/g Kcq, g/g 



^Oj, g/g 



IGNITABLE 



R1 36.84 1.83 

R2 29.07 1.49 

R3 29.20 1.52 

R5 28.88 1^ 

SELF-EXTINGUISHING 

R4 18.65 1.06 

R8 27.89 1.41 

P1 23.43 1.21 

P2 24.11 1.21 

P3 24.33 1.15 

P5 27.21 1.26 



2.88 
2.35 
2.39 
2.35 



1.66 
2.22 
1.90 
1.90 
1.80 
1.97 



the hazards tend to increase with the actual heat-release 
rate. For this reason, production constants, or beta values 
(/?x), can be calculated for a given product by the 
expression 



0x = G X /Q A - 



(?) 



Using the rate of formation of gas or smoke as a function 
of the fire size is also beneficial in comparing the 
combustion hazards of different materials. 

SMOKE PARTICLE DIAMETERS 

Measurements of both number and mass concentrations 
of the smoke provide important information relative to the 
yields (equation 4) and production constants (equation 6). 
They can also be used to calculate the average size of the 
smoke particles, using the expression 



7rd„ 



(p v ) (N ) = 1 x 10 3 M, 



O' 



(8) 



where 



p = individual particle density, g/cm , 
d = diameter of average mass, /im, 



and 1 x 10 = the appropriate units conversion 

factor. 



"»(&) 



1/3 



d m = 11.09 -S 



(9) 



when the particle diameter is expressed in micrometers. 

Using the three-wavelength smoke detector, the 
transmittance (T) of the light through the smoke can be 
calculated for each wavelength. The extinction-coefficient 
ratio can be calculated for each pair of wavelengths (A) 
from the following log-transmission ratios: 

lnTfAl.00) . lnT(A1.00) . or lnTfAO.631 
lnT(A0.63) lnT(A0.45) lnT(A0.45) 

Using these extinction coefficients and the curve in figure 
11 of reference 8, the surface mean particle size (cL^) can 
be determined. (Calculation of the extinction-coefficient 
curves assumes spherical particles with an estimated 
refractive index.) 

The smoke obscuration is the percentage of light 
absorbed by the smoke or 100% of the light minus the 
percent transmission (T). It is calculated using the 
following equation: 



Obscuration = 100(1 - T) 



(10) 



The obscuration percentages presented in this report are 
an average of those calculated from the two visible 
wavelengths, 0.45 /im and 0.63 /im. 



Assuming the approximate density of the base material to 
be 1.4 g/cm 3 , the diameter of average mass can be 
calculated from 



CONVEYOR BELT COMBUSTION RESULTS AND DISCUSSION 



The compositions of the 10 different belt types tested 
are listed in table 2. Because of their unique composition 
and construction, each belt had distinctive burning times 
and combustion products. Table 2 also lists the 
designations and burning times for each belt tested. The 
burning times were calculated from the time the burner 
was turned off until flames were no longer visible. The 
intensities of the belt fires were not considered; therefore, 
the burning times include rapid burning as well as the 
flickering flames of the quickly extinguished belts. 

All belt tests were duplicated or triplicated depending 
on the amount of sample available. The values for the 
ignitable belts listed in the following tables are averaged 
during the rapidly burning stage without the burner 
operating. Since the self-extinguishing belts did not burn 
readily, their averages may also include some residual 
effects of the burner. 

Figure 2 shows a typical ignitable belt (R5). In this 
experiment, the gas burner was turned off at 9 min. Its 



effects can be seen until the 12th minute. This belt burned 
for approximately 28 min before it self-extinguished. 
Figure 3 shows the extent of the combustion as well as the 
charring for R5. 

TABLE 2. • Conveyor belts analyzed 





Sample 


Material Burning time, 
min 


IGNITABLE 


R1 
R2 
R3 
R5 




, Styrene Butadiene Rubber (SBR) 28.5 

do 25.5 

do 51.5 

do 28.3 


SELF-EXTINGUISHING 



R4 
R8 
P1 
P2 
P3 
P5 



Neoprene (NP) 

do 

Polyvinly Chloride (PVC) 

do 

do 

do 



15.0 

17.5 

6.0 

14.5 

3.0 

7.5 




15 20 25 30 35 40 45 



80 
70 
60 



w 50 

CO 

< 



40 - 



UJ 

cc 

l_ 30 

< 

LU 

x 20 



10 



1 1 
B 


1 1 


i i i i - 






' KEY 

A Heat loss 


- \ 


1 
1 


( ' \ Mass loss 

/ 1 
/ 1 


- \ 1 


ll 
/ / 

; / 


- 




i /' 


1 


- / 


1 A 
\/ j 




/ • 

/ ±" 1 


i i 


i i i i ■ 



<M 



C" 




10 

9 

8 

7 
( 

O 
6 - 

CO 

CO 

5 o 

4 8 
< 

3 5 
2 

I 




TIME, min 



Figure 2— Results of typical ignitable conveyor belt combustion experiment A, CO and C0 2 concentrations; 
B, heat-release and mass-loss rates; C, particle mass and number concentrations; and D, diameter of average 
mass (d m ) and mean particle diameter (d 32 ). 



GAS CONCENTRATIONS AND HEAT PRODUCTION 

Figure 24 illustrates CO and C0 2 production. The 
initial spike is caused by the gas burner, which was turned 
off once the belt ignited. Several minutes were required 
for the contaminating gases to be dispersed. The belt was 
rapidly burning from the 15th to the 30th minute. 

Table 3 lists the CO and C0 2 concentrations and 
generation rates and the corresponding-heat-release rates. 
All the values for the ignitable belts are higher than those 
for the self-extinguishing belts. The CO and C0 2 
concentrations listed for the self-extinguishing belts, 
although much lower than those from the ignitable belts, 
may still include residual gas from the burner. 

Figure IB correlates the heat-release rate with the mass 
loss. As expected, the most heat was released during the 



TABLE 3. - Gas concentrations, generation rates, and 
heat-release rates for conveyor belts 





Sample 


CO, 
ppm 


co 2 , 

ppm 


G co- 
10- 2 g/s 


G co 2 ' 
9/s 


Q A , 
kW 


iNITABLE 


R1 
R2 
R3 
R5 




1,044 
778 
753 

1,032 


16,830 
14,102 
10,213 
13,940 


14.7 

10.7 

9.7 

14.6 


3.72 
3.06 
2.07 
3.09 


49.08 
38.90 
26.24 
39.31 


SELF-EXTINGUISHING 



R4 75 510 0.9 0.14 1.79 

R8 78 432 1.3 .11 1.51 

P1 62 632 .9 .14 1.79 

P2 44 637 .6 .14 1.77 

P3 213 1,405 2.9 .30 4.37 

P5 172 1,263 2.4 .28 4.14 




Scale, cm 

Figure 3.— Extent of the combustion and charring for R5. 



greatest mass loss. Most ignitable belts lost about 1 g/s 
during the rapidly burning stage. The mass-loss rates of 
the self-extinguishing belts were too small to be 
determined. 

SMOKE CHARACTERISTICS 

Figure 2C shows the typical M and N . The M rose 
slightly when the gas burner was ignited. It fluctuated 
after the burner was turned off, but shows a sustained 
increase during the rapidly burning stage. As the flames 
died, the mass concentration decreased, but increased 
again as the belt smoldered. 

The N rose steadily in response to the gas burner and 
declined after burner extinguishment throughout the 
rapidly burning and smoldering stages. Most belts, as this 
one, did not produce a distinct number concentration peak 
during the rapidly burning stage. 





TABLE 4. • 


Smoke characteristics for 


conveyor 


belts 




Sample 




4 N °' 3 


M 9 , 
mg/m 3 


d m - 








10 4 p/cm 3 


/tm 


IGNITABLE 


R1 






16.65 


91.95 


0.92 


R2 






17.59 


23.50 


.56 


R3 






20.80 


45.35 


.49 


R5 






17.21 


14.05 


.49 


SELF-EXTINGUISHING 


R4 






19.12 


5.10 


0.26 


R8 






6.02 


4.05 


.47 


P1 






29.53 


1.80 


.37 


P2 






28.02 


1.70 


.33 


P3 






ND 


.60 


ND 


P5 






35.31 


2.05 


.19 


ND 


Not determined. 









TABLE 5. - Mean particle sizes and smoke obscuration for conveyor belts 



Test 


InT(Al.OO) 
lnT(A0.63) 


InT(ALOO) 
lnT(A0.45) 


lnT(A0.63) 
lnT(A0.45) 


Average 

d 32 . 
lim 


Obscuration, 




Average, 
jim 


Range, 
lim 


Average, 
lim 


Range, 
Mm 


Average, Range, 
lim iim 


% 




R1 

R2 

R3 

R5 


0.39 
.38 
.36 
.39 


0.35 - 0.41 
.35- .39 
.34- .40 
.34- .40 


0.32 
.26 
.35 
.35 


0.22 - 0.38 
.17- .30 
.22- .50 
.34- .37 


0.26 0.15 - 0.35 
.19 .17- .24 
.41 .21 - .66 
.33 .30 - .36 


0.33 
.29 
.36 
.35 


85 
90 
75 
97 


SELF-EXTINGUISHING 



R4 0.35 0.33 - 0.37 

R8 ND NAp 

P1 ND NAp 

P2 ND NAp 

P3 ND NAp 

P5 35 .33 - .36 

ND Not determined. 
NAp Not applicable. 



0.23 


0.23 - 0.24 


ND 




NAp 


0.29 


22 


ND 


NAp 


ND 




NAp 


ND 


ND 


ND 


NAp 


ND 




NAp 


ND 


5 


ND 


NAp 


ND 




NAp 


ND 


8 


ND 


NAp 


ND 




NAp 


ND 


12 


.28 


.26- .31 


0.22 


0.17 


-0.27 


0.29 


46 



The smoke characteristics data are presented in tables 4 
and 5. A high mass concentration for belt Rl was 
reproduced in duplicate tests and so was considered valid. 
Using these data, a large calculated d^ results. 

The average particle size, d^, calculated from the three- 
wavelength transmission technique shows less variation 
than d m . The smoke obscuration must be at least 15% 
before ^ 2 can be calculated. Only two self-extinguishing 
belts, R4 and P5, produced enough smoke to secure this 
data. Since all the diameters are in the same range, there 
may not be a significant difference when comparing either 
the method of calculation or the flammability of the belts. 
Figure 2D shows the particle diameters as calculated by 
both methods. The ^ data were only calculated from the 
12th to the 33rd minute because the smoke obscuration 
was above 15% in that period. The best agreement is seen 
during the rapidly burning stage. 

COMBUSTION YIELDS 

The mass-loss rates of the self-extinguishing belts were 
too low to accurately calculate their combustion yields. 
Table 6 contains the average yields for the ignitable belts. 
The high mass concentration for Rl is once again evident. 
R3 had the highest mass-loss rate, 1.3 g/s, which 
contributes to the relatively low yields. 

PRODUCTION CONSTANTS 

Table 7 lists the production constants (or beta values). 
They are scaled according to their fire size. The 
production constants for CO and C0 2 remain fairly 
constant for all tests. However, the production constant 
for the number concentration changes considerably 
because the fire size of the flammable belts is much larger 
than for the self-extinguishing belts while the number 
concentration remains about the same. The production 
constants of all the belts for mass concentration also 
remain fairly constant because the mass concentrations 
increased proportionally with the fire size. 



SMOLDERING STAGE DATA 

For most belts, the collection of data continued after 
the visible flames had subsided. Table 8 shows the results 
of the smoldering stage. The smoldering time states the 
length of the data collection period, and does not reflect 
the complete smoldering period. 

These data were included to provide a comparison 
between the smoke characteristics of flaming and 
smoldering belts. In most belt tests, the d,,, was smaller 
during the smoldering than the flaming stage, but the 
opposite was generally true for djj. As M„ and N 
decreased, the calculated particle size decreased. 
However, as the obscuration decreased, the particles were 
slightly larger. The closest agreement with the flaming 
particle size is found when calculating (L^. 

TABLE 6. • Combustion yields for ignitable conveyor belts 





Test 


^CO' 


^co 2 < 


Y n„' 


Y M ' 






i0" 2 g/g 


9/g 


io 10 P /g 


10" 3 g/g 


R1 




17.2 


4.4 


2.2 


12.2 


R2 




13.3 


3.7 


2.3 


3.2 


R3 




8.4 


1.9 


1.5 


4.8 


R5 




16.3 


3.4 


2.2 


1.7 


TABLE 7. • Steady-state production constants for conveyor belts 




Sample 


Pco< 


^, co 2' 


*V 


*M . 






10" 3 g/kJ 


10" 2 g/kJ 


10 8 p/kJ 


I0^g/kj 


IGNITABLE 


R1 




2.99 


7.58 


3.81 


2.11 


R2 




2.76 


7.87 


4.99 


.67 


R3 




3.71 


7.91 


8.19 


1.79 


R5 




3.71 


7.86 


4.94 


.40 


SELF-EXTINGUISHING 


R4 




7.84 


8.38 


159.73 


4.26 


R8 




8.61 


7.28 


51.49 


3.46 


P1 




4.83 


7.75 


184.06 


1.12 


P2 




3.45 


7.85 


175.55 


1.07 


P3 




6.61 


6.86 


ND 


.15 


P5 




5.80 


6.76 


96.12 


.56 


ND 


Not determined. 











10 









TABLE 8. 


- Smoldering 


data for conveyor 


belts 








Sample 


Smoldering 
min 


time, 


1C 


4 N °' S 

i 4 p/cm 3 


M 9'3 
mg/nr 


/tm 


d 32> 


Obscuration, 
% 


IGNITABLE 


R1 . .. 
R2 ... 
R3 1 . . 




2.0 

7.5 

ND 

20.0 






2.43 

2.94 

ND 

18.58 


1.24 
1.33 
ND 
1.58 


0.47 
.45 
ND 
.24 


0.39 
.30 
ND 
.29 


16 
28 
ND 


R5 ... 




48 


SELF-EXTINGUISHING 



R4 12.0 

R8 10.0 

P1 3.3 

P2 3.5 

P3 1.5 

P5 3.0 

ND Not determined. 

'Smoldering stage data were not collected. 



40.03 


6.85 


0.32 


0.30 


19 


3.82 


1.36 


.34 


ND 


ND 


29.01 


8.48 


.28 


ND 


ND 


9.69 


1.58 


.27 


ND 


ND 


29.50 


1.74 


.23 


ND 


ND 


29.67 


2.22 


.19 


.31 


35 



COMPARISON OF MATERIALS TESTED 



Smoke detection has been raised to a high level of 
sophistication in order to detect fires in their earliest 
stages, and to discriminate between actual fires and 
emissions that are not fire related. In this effort, the 
smoke characteristics of various materials have been 
analyzed. Earlier studies of wood, coal, and transformer 
fluid were conducted in the same intermediate-scale fire 
tunnel using the same instrumentation and calibration 
techniques. The different combustion kinetics of each 
material tested necessitated a modification of some of the 
experimental conditions such as ventilation rates and 
ignition sources (table 9). 

The gas, heat, and smoke concentrations for the four 
materials studied are found in table 10. The highest gas 
concentration was produced by the ignitable conveyor 
belts, but the highest heat release was produced by wood 
fires. The configuration of the wooden sticks may have 
improved the air circulation, which could have supported 
more complete combustion than was achieved using the 
other fuels. For better comparison, the emission products 
of the other fuels were adjusted, based on their production 
constants, to the level of the wood fires. 

Table 11 gives normalized values of the data in table 10. 
At this projected fire intensity, burning coal generally 
produced the most hazardous emissions. However, the 
true assessment of the hazards of burning materials cannot 
be determined solely on their emission products. Their 
physical characteristics and composition must also be 
considered. For example, the extremely rapid growth rate 
and thick smoke of liquid fuels fires such as transformer 
fluid increases their potential danger. By comparison, the 
combustion of the synthetic components of PVC conveyor 
belts may produce high levels of toxic gas and smoke, but 
because they self-extinguish their relative dangers are 
reduced. An estimation of the potential danger of burning 



materials must not only include their smoke characteristics, 
but also the toxic environment that their combined 
emissions may create. 

Most smoke detectors sense an increase in the number 
and size of the particulate matter. In these experiments, 
burning conveyor belts produced a thick smoke obscuring 
on an average 87% of the light. The particle size of the 
flammable belts tended to be larger than the other 
materials tested. The particle size and obscuration values 
are listed in table 12. The higher the smoke concentration 
the more dangerous are the effects from a fire, but the 
more detectable it becomes. 

The production constants (table 13) use the heat release 
to compare the rate of formation of gas or smoke. 
Burning coal generated the highest number of smoke 
particles, and transformer fluid generated the largest mass 
concentration. Since ignitable belts burn with such a high 
heat release, the production constants remain relatively 
low especially for M and N . 

All combustion generates some amount of smoke. The 
characteristics of this smoke depend not only upon the 
composition of the material, but the conditions in which it 
is burning. In an attempt to standardize these 
experiments, conditions may have been used that were not 
optimum for all materials. These limitations must be 
considered when comparing the gas concentrations and 
smoke characteristics given in this report. 

TABLE 9. - Ignition source and ventilation rates 



Material 


Ignition source 


VA. m 3 /s 


Wood 

Coal 

Transformer fluid . . . 
Conveyor belts 


Natural gas burner . . 

Electric strip heaters . 

Natural gas burner . . 

... do 


1.0 
.24 
.47 
.11 



TABLE 10. - Gas, heat, and smoke concentrations 



TABLE 12. - Particle size and smoke obscuration 



Material 



CO, CO,, 



N„ 



M Q , 



WW, WW£| >*A, A O' -X O' 

ppm ppm kW 10 p/cm mg/m 



Material 



Wood 145 6,759 110.2 6.0 49.1 

Coal 89 1,095 5.9 1.5 11.4 

Transformer fluid 113 1,769 21.1 1.1 35.3 

Ignitable belts 902 13,771 38.4 .2 43.7 

Self-extinguishing belts 107 813 2.6 .2 2.6 



TABLE 11. - Normalized gas and smoke concentrations 

Material CO CO^ N^ Ml 

ppm ppm 10 6 p/cm 3 mg/m 3 

Wood 145 

Coal 441 

Transformer fluid .... 284 

Ignitable belts 294 

Self-extinguishing belts 528 



6,759 


6.0 


49.1 


5,762 


7.12 


50.6 


4,992 


2.79 


85.2 


5,017 


.01 


13.5 


4,480 


1.08 


12.1 



Mm 



u 32' 



Obscuration, 
% 



Wood 

Coal 

Transformer fluid .... 

Ignitable belts 

Self-extinguishing belts 
ND Not determined. 



0.22 
.21 
.39 
.62 
.32 



ND 
0.23 
.39 
.33 
.29 



9 
20 
46 
87 
18 



TABLE 13. - Production constants 



Material fi co , p CQ2 , 0^, Mq , 

10" 3 g/kJ 10" 2 g/kJ 10 10 p/kJ 10"* g°/kJ 

Wood 1.6 10.4 5.79 4.9 

Coal 4.8 8.9 6.83 4.7 

Transformer fluid .... 3.1 7.7 2.48 7.8 

Ignitable belts 3.2 7.8 .05 1.2 

Self-extinguishing belts 5.8 6J) 1.04 1.1 



CONSIDERATIONS 



Burning materials generate unique and dangerous 
combustion products. In a mine fire, these emissions 
combine to produce a wide variety of smoke particles and 
volatile gases that are transported by the ventilating 
system. If the individual smoke characteristics and 
combustion products were known, more discriminating or 
sensitive smoke detectors could be developed. For 
example, the presence of exhaust emissions could be 
distinguished from the products of a real fire, eliminating 



many false alarms. Thus, the remaining alarms would 
elicit an immediate response instead of a delay caused by 
the need to confirm the alarm. This would further the 
efforts of the Bureau to improve health and safety 
conditions in mines. With this goal in mind, these 
experiments were conducted to compare the potential 
detectability of the smoke generated by combustible 
materials found in underground mines. 



REFERENCES 



1. Egan, M. R., and C. D. Litton. Wood Crib Fires in a Ventilated 
Tunnel. BuMines RI 9045, 1986, 18 pp. 

2. Egan, M. R. Transformer Fluid Fires in a Ventilated Tunnel. 
BuMines IC 9117, 1986, 13 pp. 

3. . Coal Combustion in a Ventilated Tunnel. BuMines 

IC 9169, 1987, 13 pp. 

4. Sapko, M. J., K. E. Mura, A. L. Furno, and J. M. Kuchta. Fire 
Resistance Test Methods for Conveyor Belts. BuMines RI 8521, 1981, 
27 pp. 

5. Lee, C. K., R. F. Chaiken, J. M. Singer, and M. E. Harris. 
Behavior of Wood Fires in Model Tunnels Under Forced Ventilation 
Flow. BuMines RI 8450, 1980, 58 pp. 



6. McCaffrey, B. J., and G. Heskestad. A Robust Bidirectional 
Low-Velocity Probe for Flame and Fire Application. Combust, and 
Flame, v. 26, No. 1, 1976, pp. 125-127. 

7. Patashnick, H., and G. Rupprecht. Microweighing Goes On-Line 
in Real Time. Res. and Dev., v. 28, No. 6, 1986, pp. 74-78. 

8. Cashdollar, K. L., C. K. Lee, and J. M. Singer. 
Three-Wavelength Light Transmission Technique To Measure Smoke 
Particle Size and Concentration. Appl. Optics, v. 18, No. 11, 1979, 
pp. 1763-1769. 

9. Tewarson, A. Heat Release Rate in Fires. Fire and Mater., 
v. 4, No. 4, 1980, pp. 185-191. 



12 



APPENDIX.-SYMBOLS USED IN THIS REPORT 

Cx conversion factor of given combustion product 

d,,, diameter of a particle of average mass, /xm 

d3 2 mean particle size, jum 

G x generation rate of a given combustion product, g/s 

H A actual heat of combustion, kJ/g 

H c net heat of combustion of material, kJ/g 

Hcq heat of combustion of CO, kJ/g 

K x theoretical yield of a given gas, g/g 

In logarithm, natural 

M f fuel mass loss rate, g/s 

M particle mass concentration, mg/cm 3 

M x density of a given gas, g/(m 3 «ppm) 

N particle number concentration, p/cm 3 

p particle 

Q A actual heat-release rate, kW 

T transmission of light 

VpA,, ventilation rate, m 3 /s 

Y x yield of a given combustion product, g/g or p/g 

)3 X production constant of a given combustion product, g/kJ or p/kJ 

AX measured change in a given quantity, ppm 

A wavelength, ixm 



p individual particle density, g/cm 



* U.S. GOVERNMENT PRINTING OFFICE: 611-012/00,022 

INT.-BU.OF MINES,PGH.,PA.28805 

C US 



-Q 


J-OOTJODC 


m 

z 


w 


O 


II 


CD ■ 


So 


O" 

c 

.73 


O 


uction 
irans 1 


c CD 


<5 


CO 


X 


o -o 


ICIAL 1 

FOR PR 


> 
oi 


00 

o 
o 


& Distr 
Mill Roa 


rtment c 
Mines 


<_ 00 i 

> c 1 


CO 




Q- ex 
c 


13" 


H 00 






5' 

3 


CD 


™2 






5" 


«S 








CD 


I w 








o" 

"1 


CO 










o 










o 











m 
O 

c 
> 

i - 

o 

■v 
-o 
O 

3D 



3 

m 



O 

-< 
m 

3 



«< ^%_ ■ 




^r - 










^ 



'^ty 




•*• A* °^ "■« A° V. *oTo' .ft* ^ *,v 




i><*. 



**'*« 






O J1 




" * V *V 
%7 ^,* * 

'X ,*»^^^^ 





5^ 




*p^. : 




^°* 




\ ""'V ... . v*^>* **♦ '*—•• f ° v % 













$&£* ** ^ -WW ^ ^ *-^P/ ** *« v«w ft<^ ^«Sf.° ^-^ 


































•^^•x 

^ ^ 













• *^ v \ '°f?P^ /\ IW^ : *^ v % '-W^ : **% 




^oV* 



5,°-^. 







v-o 5 




n-' <** * > **J S \« ft." o *• - 



.<■". 



O v . » o 








* 



O V 



^ 4? a*j^>*> > v N *i,'.r* cj* 4? ••^L'* *> a "'*°' <^ aO v .»••'♦ *> 



47 ^ 






IP's 



4- <tJ ' 



A <* *o . * • .0* 



* o 



^ '°.»° A& ^ ""'Tit 4 A 






A « 



Lf* ^ v *v- ^ 4? 



^ 



v ^ 






^ "*. 






^ v^V %^-'/ v 7 ^'** c 




^- A 



J ^G= 

" A^* 







f/ A^* 




G* % '<r.T* • <v 







Uz* V /Jlfe'-, **^ .-SsKai-. \/ /Jte\ ♦*.♦♦ • 







°^. * * • "■ * A. V, * o » o ' 

y*'. %> 4,° v »irfj£» ^ 
'.* f ^ •% '.5»P.' * v "^W ,/\ *.s8*- ** V ^ l W^' : /> 

^^^•/ %^^/ V^/ v^V° v^*\/ V*- 








*bv D 







»* ^ 














,/% 




-0 V 














4 o 




>.o* V ^ 



^'^-/ v^^'y v^-/ ^^^^z v^v \- 



BOOKBINDING i 
J Verch -Aco' 19 



\ ***** * 



b. %T.T* A 



.6* ^ *.^T*' A 




^n. ^ 



<j^ A 





I 



mmf\ 



Saw 



mm 
I 

Bin 

I 



